This avoids weirdness when 'fc -e vi' or the like is done and there is a
syntax error in the file. Formerly an interactive shell tried to execute
stuff after the syntax error and exited.
This should also avoid similar issues with 'command eval' and 'command .'
when 'command' is implemented properly as in NetBSD sh.
Special builtins did not have this problem since errors in them cause the
shell to exit or to reset various state such as the current command input
file.
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